1. Field of the Invention
This invention relates to a piston ring for use in pistons for internal combustion engines. In particular, the invention relates to a through-hardened steel piston ring having a generally rectangular or keystone cross-section, and which has been coated via deposition, plating or thermal spraying with a coating.
2. The Prior Art
Piston rings are often coated with a ceramic or other coating via various deposition process, such as PVD, or thermal spray techniques, to improve their wear resistance. These rings are often case hardened prior to coating using a nitride or carburize process. Such processes via heat treatment case hardens a depth from the outer surface of the ring while leaving the untreated interior of the ring at a much lower hardness and close to the green stock wire. This leads to a harder surface of the ring yet allows the ring to have enough flexibility to function in the piston and allow for easy shaping before the case hardening treatment. One drawback of the case hardened piston rings is that their case hardening lowers the fatigue resistance and can lead to cracking of the piston ring. Therefore, it would be desirable to create a piston ring that increases the fatigue strength and wear resistance of the ring.